"To the degree that she
There is pride to make oneself pretty. If a person is told how pretty or handsome they are enough times, the head swells and the (pretty) person becomes GLORIFIED. Contrast this with Hebrews 5:1-5-10 .... Christ was NOT GLORIFIED in this manner.
To LIVE SENSUOUSLY has strong sexual overtones. After all, this Babylon did play the HARLOT with the kings of the earth (verse 3).
to the same degree give her TORMENT and MOURNING;
TORMENT here is TORTURE to a maximum of pain. Symbolically, it is the kind of flame that is forever burning in Hades (Luke 16:19-24-31). With the maximum spiritual pain comes the MOURNING. This is in direct contrast to the new heaven and new earth (Revelation 21:4).
for she says in her heart,
'I sit as a QUEEN and I am not a WIDOW, and will never see MOURNING.'
This phrase is used in Isaiah 47:1-11. This prophesy may have been directly given for this endtime.
The phrase 'says in her heart' denotes this is a huge spiritual denial. This isn't reality she is looking at but rather a boastful pride which counts on the king(s) of the earth to keep her status as QUEEN. One could interpret this as 'the government will take care of us (spiritually too)'. Obviously, her role as QUEEN lasts only as long as the king(s) want her to last (verses 9 and 10). In the Mideast, inheritance and status comes through the male side of the family. This Babylonian woman brags that she never will lose her husband(s) and hence see MOURNING.
In the Old Testament, when Jerusalem forgot God, Jeremiah compares Jerusalem as a WIDOW (Lamentations 1:1-11). In similar manner, we, believers, are the bride of Christ (Revelation 21:9); however, ours is eternal life and not this QUEEN's false bravado as the next verse shows.